1. Field of the Invention
The present invention generally relates to a viscous fluid type heat generator in which heat is generated by forcibly shearing a viscous fluid confined in a chamber and the heat is transmitted to a heat exchanging liquid circulating through a heating system. More particularly, the present invention relates to a viscous fluid type heat generator used as a heat source, for supplying heat to a heating system, provided with an ability to maintain a reliable heat-generating performance during the operation of the heating system.
2. Description of the Related Art
Japanese Unexamined (Kokai) Utility Model Publication No. 3-98107 (JU-A-3-98107) discloses a viscous fluid type heat generator adapted for being incorporated into an automobile heating system as a supplemental heat source. The viscous fluid type heat generator of JU-A-3-98107 is formed as a heat generator provided with a unit for changing a heat-generating performance. The heat generator of JU-A-3-98107 includes front and rear housings connected together to form a housing assembly in which a heat generating chamber, for holding a viscous fluid, and a heat receiving chamber, arranged adjacent to the heat generating chamber to allow a heat exchanging liquid to receive heat from the heat generating chamber, are formed. The heat receiving chamber in the housing assembly allows the heat exchanging liquid to flow therethrough from a liquid inlet port to a liquid outlet port formed in a portion of the housing assembly. Namely, the heat exchanging liquid is circulated through the heat receiving chamber and a separate heating circuit of the automobile heating system so as to supply heat to the objective area, e.g., a passenger compartment of the automobile, during the operation of the heating system. The heat exchanging liquid flows into and out of the heat receiving chamber through the liquid inlet port and the liquid outlet port. The heat generator of JU-A-3-98107 further includes a drive shaft rotatably supported by bearings which are seated in the front and rear housings of the housing assembly. A rotor element is mounted on the drive shaft so as to be rotated together with the drive shaft within the heat generating chamber. The inner wall surface of the heat generating chamber and the outer surfaces of the rotor element define labyrinth grooves in which the viscous fluid, such as silicone oil having a chain-molecular structure, is sheared to generate heat, in response to the rotation of the rotor element.
The heat generator of JU-A-3-98107 has a characteristic arrangement such that upper and lower housings are attached to a bottom portion of the housing assembly to form a heat generation control chamber therein. The heat generation control chamber is formed as a volume-variable chamber having a wall consisting of a membrane such as a diaphragm.
The heat generating chamber communicates with the atmosphere via a through-hole bored in an upper portion of the front and rear housings of the housing assembly and with the heat generation control chamber via a communicating channel arranged between the heat generation control chamber and the heat generating chamber. The volume of the heat generation control chamber is adjustably changed by the movement of the diaphragm which is caused by a spring element having a predetermined spring factor or an externally supplied signal such as a pressure signal supplied from an engine manifold of an automobile.
When the drive shaft of the heat generator of JU-A-3-98107 incorporated in an automobile heating system is driven by an automobile engine, the rotor element is rotated within the heat generating chamber, so that heat is generated by the viscous fluid, to which a shearing force is applied, between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. The heat generated by the viscous fluid is transmitted from the heat generating chamber to the heat exchanging liquid, i.e., engine-cooling water circulating through the heating system and carried by the water to a heating circuit of the heating system to warm an objective heated area such as a passenger compartment.
When it is detected that the objective area is excessively heated with respect to a reference temperature value predetermined for that area, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved in response to a vacuum pressure signal supplied from the engine manifold to increase the volume of the heat generation control chamber. Accordingly, the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber to reduce the generation of heat by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. Therefore, the heat generating performance can be reduced, i.e., the application of heat to the objective heated area is reduced.
When it is detected that heating of the objective heated area is excessively low with respect to the predetermined reference temperature value, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved by the pressure signal and by the spring force of the spring element to reduce the volume of the heat generation control chamber. Therefore, the viscous fluid contained in the heat generation control chamber is supplied into the heat generating chamber so as to increase the heat generation by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. As a result, the heat generating performance can be increased, i.e., application of heat to the objective heated area is increased.
Nevertheless, in the viscous fluid type heat generator having a variable heat generating performance and disclosed in JU-A-3-98107, when the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber, the atmospheric air is introduced from the through-hole of the housing assembly into the heat generating chamber so as to prevent a vacuum occurring in the heat generating chamber due to the withdrawal of the viscous fluid therefrom. Thus, the viscous fluid must come into contact with the atmospheric air when a change in the heat generating performance occurs, and is eventually oxidized. Therefore, a gradual degradation of the heat generating characteristics of the viscous fluid occurs. Further, the above-mentioned through-hole formed in the housing assembly permits a certain amount of moisture from the atmosphere to enter into the heat generating chamber of the heat generator, and accordingly, the heat generating performance of the heat generator is adversely affected by the moisture within the heat generating chamber.
Further, the viscous fluid type heat generator of JU-A-3-98107 is not internally provided with a mechanism or a means for conducting an appropriate replacement of the viscous fluid between the heat generating chamber and the heat generation control chamber. Thus, when the drive shaft is continuously rotated at a high speed without withdrawing the viscous fluid from the heat generating chamber into the heat generating control chamber, the viscous fluid confined in the heat generating chamber is continuously subjected to a shearing action by the rotor element to be heated to an extremely high temperature at which the physical property of the viscous fluid is degraded to reduce its heat generation performance.
U.S. Pat. No. 4,974,778, and the corresponding German laid-open publication DE-3832966, disclose a different type of heating system, for a vehicle with a liquid-cooled internal combustion engine, which includes a viscous fluid type heating unit. The viscous fluid type heating unit of U.S. Pat. No. '778 includes a housing defining a heat generating chamber or a working chamber having a through-opening, and a heat generation control chamber or a viscous fluid supply chamber communicating with the heat generating chamber via the through-opening. The heat generating chamber and the heat generation control chamber are not formed as chambers directly opening toward the atmosphere and, therefore, degradation of the viscous fluid due to the air and an adverse affect on the heat generating performance due to the moisture can be avoided. Further, the through-opening between the heat generating chamber and the heat generation control chamber is closed and opened by a spring-operated closing means, and accordingly, the degradation of the viscous fluid can be avoided even after long use of the heating unit or after high speed continuous operation of the heating unit.
The rotor element of the heating unit of U.S. Pat. No. '778 is formed as a wheel with a cup-shaped cross-section. Thus, the axial length of the rotor element is relatively large and increases the entire axial length of the heating unit. As a result, the mounting of the viscous fluid type heating unit in a vehicle at a position suitable for receiving a drive power from the vehicle internal combustion engine may be difficult.
European Patent Publication No. 0687584 A1 (EP-A-'058 A1) discloses a fluid-frictional type heat generator in which a disc-shape rotor element is rotated in a tightly closed and viscous fluid-filled heat generating chamber. The disc-shaped rotor element is provided with front and rear main end faces to provide the viscous fluid with a shearing action to frictionally generate heat, and the axial length of the rotor element is relatively small. Therefore, the mounting of the fluid-frictional type heat generator of EP-A-'584 A1 in a vehicle can be easy. Further, the heat generating chamber of EP-A-'584 A1 is tightly closed against the atmosphere, and accordingly, the viscous fluid in the heat generating chamber is not exposed to the fresh air, and the heat generating chamber does not permit any moisture to enter therein. Therefore, degradation of the viscous fluid does not occur, and the heat generating performance of the heat generator is not adversely affected by the moisture.
Nevertheless, in the fluid-frictional type heat generator of EP-A-'584 A1, heat generating gaps filled with the viscous fluid are formed between the opposite flat end faces of the disc-shape rotor element and the facing flat inner wall faces of the heat generating chamber, and between the outer circumference of the rotor element and the facing circular inner wall face of the heat generating chamber. Therefore, the heat generating gaps on both sides of the rotor element, i.e., a front heat generating gap and a rear heat generating gap can communicate with one another only via the heat generating chamber annularly extending around the outer circumference of the rotor element, i.e., an annular heat generating gap and, accordingly, the viscous fluid in the front heat generating gap on the front side of the rotor element is not permitted to flow toward the rear heat generating gap on the other rear side of the rotor element due to the existence of the small annular heat generating gap between the front and rear heat generating gaps. Consequently, even if the viscous fluid in each of the front and rear flat heat generating gaps of the heat generating chamber individually moves in its own heat generating gap, there occurs no fluid circulation between the heat generating gaps on both sides of the rotor element. Therefore, the viscous fluid in the heat generating chamber must gradually be degraded during the operation of the heat generator. Moreover, if the amounts of the viscous fluid in the front and rear heat generating gaps in the heat generating chamber are different from one another, degradation of the smaller amount of viscous fluid occurs more quickly than that of the larger amount of viscous fluid, and accordingly, the heat generator cannot exhibit a stable heat generating efficiency over a long operating life.